The present invention relates generally to the field of direct current (xe2x80x9cDCxe2x80x9d) motors and particularly to the estimation of DC motor brush wear. While this disclosure emphasizes embodiments applicable to diesel-electric locomotives, it will be obvious to one of ordinary skill in the art that embodiments of the present invention are also useful in a wide variety of other contexts.
Diesel-electric locomotives utilizing DC motors make up a significant portion of many railroad locomotive fleets. A DC motor passes current to a rotating mechanical commutator through electrically conductive parts known as brushes. The brushes wear with use, and the amount of brush wear is measurable as the decrease in brush length occurring during a time interval of interest. Neglecting to replace the brushes before they have completely worn out can result in complete motor failure. Such failures, especially when occurring far from a repair shop (xe2x80x9croad failuresxe2x80x9d), can be costly and disruptive of normal railroad operation.
To avoid this cost and disruption, railroads have adopted conservative preventive maintenance policies scheduling brush replacement well before the brushes are likely to be completely worn out. Choosing the timing of scheduled brush replacement, however, can be a difficult task: if too frequent, the cost of labor to remove and install brushes, of lost revenue while the locomotive is out of service, and of the replacement brushes themselves becomes excessive; if too seldom, the cost of road failures becomes excessive. To facilitate brush replacement scheduling, therefore, railroads have considered various approaches to estimating brush wear. These approaches include manual inspection, in service electronic sensing, and estimation from environmental variables (xe2x80x9cEEVxe2x80x9d).
Of these approaches, as conventionally practiced, manual inspection is most accurate, but also labor intensive and therefore most expensive; in service electronic sensing promises intermediate accuracy and intermediate cost, owing to additional sensors and cabling, but is still largely in the experimental stage of development; and EEV, while least expensive to implement and available today, conventionally realizes the poorest accuracy owing to the use of only a single environmental variable, typically locomotive mileage, for the estimation. An opportunity exists to improve the accuracy of brush life EEV by utilizing multiple environmental variables, thereby achieving an accuracy approaching that of manual inspection at a cost approaching that of conventional EEV.
The opportunity described above is addressed, in one embodiment of the present invention, by an apparatus for estimating DC motor brush wear comprising: a wear element calculator adapted to calculate a plurality of wear elements from at least one environmental variable; a wear element multiplier adapted to multiply the wear elements by respective ones of a plurality of wear coefficients to yield a plurality of weighted wear elements; and a summer adapted to sum the weighted wear elements to yield a brush wear estimate.